The present invention relates to a grid for a battery plate which is produced by a rotary expander, a method of producing it, and a battery using it.
A battery plate of a lead storage battery is configured by filling an active material into meshes of a grid made of lead or a lead alloy. Such a grid is often produced by directly forming a grid-like shape by means of, for example, casting of lead or a lead alloy, or alternatively by forming meshes in a metal sheet made of lead or a lead alloy (hereinafter, a sheet such as that containing lead, a lead alloy, or another alloy is referred to merely as a metal sheet) by an expander. The expander is of the reciprocal type in which meshes are sequentially formed in a metal sheet with starting from both the ends of the sheet, by vertical motions of a die cutter, or of the rotary type in which slits are formed in a zigzag pattern by rotation of a disk cutter, and the metal sheet is stretched from both the sides to develop the slits into meshes. As shown in FIG. 37, in a disk cutter 1 which is used in the rotary expander, large numbers of ridges 1a and valleys 1b are alternately formed at regular intervals along a circumferential direction on the peripheral side face of a metal disk. The valleys 1b are curved faces consisting of the circumferential face itself constituting the peripheral side face of the disk of the disk cutter 1. The oval enlarged view in FIG. 37 shows the circumferential face in a form developed to a plane. Each of the ridges 1a is formed by protruding the circumferential face of the disk cutter 1 in a ridge-like shape toward the outer periphery. The apex of the ridge is rounded and formed with being shifted toward the front side in the rotational direction (indicated by the arrow in the figure).
In the disk cutter 1, grooves 1c are formed in both the disk-like faces and in every other valley 1b. Each of the grooves 1c is a groove which has a width that is equal to the length (the distance between adjacent ridges 1a) of the corresponding valley 1b, and a depth that is about one half of the thickness of the valley 1b (the thickness of the disk cutter 1), and which is radially formed in the disk face of the disk cutter 1. The groove 1c is formed so as to open in the valley 1b in the outer peripheral side and have a length of some degree toward the center. The grooves 1c which are formed in every other valley 1b are arranged so as to be alternate on both the faces.
A large number of such disk cutters 1 are arranged on a common rotation shaft with being separated from each other by a distance which is approximately equal to the thickness of the disk cutters 1, thereby forming a disk cutter roll. As shown in FIG. 38, two disk cutter rolls each configured by a large number of such disk cutters 1 are vertically arranged, and a lead sheet 2 is passed between the rolls, thereby forming slits 2a. In this case, as, shown in FIG. 39(a), the upper and lower disk cutter rolls are placed respectively at levels which allow the valleys 1b of the upper and lower disk cutter 1 to slightly overlap with each other. Furthermore, the upper and lower disk cutter rolls are placed with being shifted in the axial direction by a half pitch so that each of the disk cutters 1 of the lower disk cutter roll is positioned between the disk cutters 1 of the upper disk cutter roll. The rotational phase is adjusted so that, when the valley 1b in which the groove 1c is formed in one disk face of the upper disk cutter 1 reaches the lower end, the valley 1b in which the groove 1c is formed in the other disk face of the lower disk cutter 1 reaches the upper end, and, when the ridge 1a of the upper disk cutter 1 reaches the lower end, as shown in FIG. 39(b), the ridge 1a of the lower disk cutter 1 reaches the upper end.
When a metal sheet 2 is passed between the disk cutter rolls, as shown in FIG. 38, the slits 2a are formed in the metal sheet 2 by the ridges 1a of the upper and lower disk cutters 1, and thin wires 2b between the slits 2a which are formed adjacently in the width direction of the metal sheet 2 are pressed by the upper and lower ridges 1a to alternately vertically protrude in a ridge-like shape. As shown in FIG. 39(a), in the valleys 1b of the upper and lower disk cutters 1 where the grooves 1c face each other in opposite directions, the metal sheet 2 is cut so that the slits 2a are continuously formed, and, in the valleys where the grooves 1c face each other, the metal sheet 2 is not cut so that the slits 2a are intermitted to form nodes 2c. In the metal sheet 2, therefore, the slits 2a each having a length corresponding to two ride-like shapes which are formed by pressing of the ridges 1a are continuously formed in the transportation direction while being intermitted in the nodes 2c. Adjacent ones of the slits 2a are similarly continuously formed while their nodes 2c are shifted from each other by a half pitch. Therefore, the slits 2a are formed in a zigzag pattern as shown in a plan view which is in a circle of FIG. 38.
The metal sheet (lead sheet) 2 in which the many slits 2a are formed as described above is stretched toward both the sides in the width direction in a subsequent step. As a result, as shown in FIG. 40, the slits 2a are widened so as to form meshes, whereby a lattice-like grid is formed in which the nodes 2c are connected to one another by four wires 2b that are obliquely bent to be drawn out.
As shown in FIG. 47, endmost disk cutters 4 are disposed on both the axial ends of the lower disk cutter roll, respectively. In each of the endmost disk cutters 4, as shown in FIGS. 48 and 49, ridges 4a and valleys 4b are alternately arranged in the peripheral edge. The valleys 4b, and grooves 4c which are formed in the valleys 4b are configured in the strictly identical manner as the valleys 1b and the grooves 1c of the usual disk cutters 1. In each of the ridges 4a, however, a peripheral side face configured by a reference circumferential face is formed. Namely, in the endmost disk cutters 4, the ridges 4a do not protrude in a ridge-like shape toward the outer periphery, and the valleys 4b do not have a shape which is relatively recessed with respect to the ridges 4a. The endmost disk cutters 4 are placed at the ends of the lower disk cutter roll so as to be outward juxtaposed with the usual disk cutters 1 at the ends of the upper disk cutter roll, respectively.
In the ends of the disk cutter rolls, as shown in FIG. 47(b), the ridges 4a of the endmost disk cutters 4 of the lower disk cutter roll overlap with the ridges 1a of the end disk cutters 1 of the upper disk cutter roll, whereby the metal sheet 2 between the ridges are cut so that the slits 2a are formed and the wires 2b downward protrude in a ride-like shape. As shown in FIGS. 47(a) and 47(c), also in the adjacent portions (the right end in FIG. 47(a), and the left end in FIG. 47(b)) where the grooves 4c of the valleys 4b of the lower endmost disk cutters 4, and the grooves 1c of the valleys 1b of the upper end disk cutters 1 face each other in opposite directions, the valleys 1b and 4b slightly overlap with each other, whereby the metal sheet 2 is cut and the slits 2a are continuously formed. However, in the adjacent portions (the left end in FIG. 47(a), and the right end in FIG. 47(b)) where the grooves 4c of the valleys 4b of the lower endmost disk cutters 4, and the grooves 1c of the valleys 1b of the upper end disk cutters 1 are formed in the opposed faces so as to face each other, the grooves 1c and 4c cause the peripheral side faces of the valleys 1b and 4b not to overlap with each other, and the metal sheet 2 is not cut. Therefore, endmost nodes 2f which are similar to the nodes 2c are formed. Since no slit 2a is formed in the outer end, the endmost nodes 2f are directly connected to frame portions 2g which are formed in the ends in the width direction of the metal sheet 2.
The metal sheet 2 in which the many slits 2a are formed as described above is stretched toward both the sides in the width direction in the subsequent step of the rotary expander. As a result, as shown in FIG. 50, the slits 2a are widened so as to form meshes, whereby a lattice-like grid is formed in which the nodes 20 and the endmost nodes 2f are connected to one another by four wires 2b that are obliquely drawn out. In practice, the nodes 2c are pulled by the wires 2b during the developing step to be inclined in a twisting direction. In FIG. 50, however, such twist is omitted and the grid is diagrammatically shown.
Problem (1) to be Solved by the Invention
In the conventional grid described above, when the slits 2a are formed in the metal sheet 2, the wires 2b connected to each of the nodes 2c are pressed by the ridges 1a to be bent in the basal end. During a process of developing the slits 2a into a lattice-like shape, the tensile stress applied to the wires 2b is concentrated in the basal end where the wires are connected to the node 2c. When stress is concentrated in the basal end of the node 2c, an excessive load is applied to the basal end during the developing process, and rupture may occur in the basal end. Therefore, corrosion due to electrolyte easily advances with starting from the basal end, thereby causing the possibility that a crack of corrosion occurs in the wires 2b during use of a battery.
Consequently, a conventional grid which is produced by using a rotary expander has a problem in that a basal end where a wire is connected to a node is cracked by corrosion and the life of a battery is shortened.
Problem (2) to be Solved by the Invention
In the conventional disk cutter 1 configured as described above, as shown in FIG. 41, each of the ridges 1a is not formed as a ridge having an isosceles triangular shape, but formed into a scalene triangular shape in which the apex 1i is formed with being shifted toward the front side in the rotational direction. The rotating disk cutter 1 forms the slits 2a in the metal sheet 2, and presses the fence-like portion between the slits 2a by the ridges 1a to project the portion in a ridge-like shape, thereby forming the wires 2b. In the case where the ridges 1a have an isosceles triangular shape, therefore, the front half of the fence-like portion between the slits 2a protrudes in a ridge-like shape while being gradually stretched by the apexes 1i of the ridges 1a, and in contrast the latter half is pressed only by the rear slopes of the ridges 1a which are in rear of the apexes of the ridges 1a. In each of the wires 2b between the slits 2a and protruding in a ridge-like shape, consequently, the front half is more elongated to be thinned. When a grid is formed by stretching such wires, there arises a defect that walls of the meshes are uneven in thickness. By contrast, when the apex 1i of each ridge 1a is formed with being shifted toward the front side, the fence-like portion between the slits 2a is first pressed by a substantially whole front area of the slope which is raised by a steep angle θ10 of the front side, so as to protrude at a relatively early timing to form the wires 2b. In accordance with the rotation, also the rear area gradually protrudes. As a result, the whole wires 2b are uniformly extended and the thickness is even. Because of the above, conventionally, a rotary expander uses the disk cutter 1 in which the apex 1i of the ridge 1a is formed with being shifted toward the front side in the rotational direction (see Japanese Patent Publication (Kokoku) No. SHO59-35694).
The metal sheet 2 in which the many slits 2a are formed as described above is stretched toward both the sides in the width direction in a subsequent step, whereby the slits 2a are widened to form rhombic meshes, with the result that a grid for a battery plate is formed.
With respect to the angles at which the slopes on both the sides of the apex 1i of each ridge 1a are connected to the valleys 1b, the front angle θ10 is steeper than the rear angle θ20. As shown in FIG. 42, also in each of the wires 2b which are formed as a result of protrusion of the fence-like portion between the slits 2a of the metal sheet 2 in a ridge-like shape, therefore, the front bending angle θ11 is steeper than the rear bending angle θ21. When the metal sheet 2 is stretched to widen the slits 2a to form meshes, therefore, the degree of cut into the nodes 2c is large or the strength is reduced in the front end where the wires 2b between the slits 2a are sharply bent. As a result, as shown in FIG. 43, there arises the possibility that the length of the nodes 2c is reduced, or rupture occurs in edge portions (edge portions D in FIG. 43). In FIG. 43, twisting is not shown, and the grid is schematically shown.
When a grid for a battery plate is produced by using the disk cutters 1 of a conventional rotary expander, particularly in the case where the grid is used as a positive plate, the nodes 2c of the meshes and the edge portions D are corroded by electrolyte with starting from rupture or the like to cause a crack of corrosion, thereby producing a problem in that the capacity of a lead storage battery is reduced or the life of the battery is shortened.
Problem (3) to be Solved by the Invention
As shown in FIG. 44, the wires 2b are pressed by the ridges 1a of the disk cutters 1 to be elastically deformed in a ridge-like shape in which the apex 2e is bent at the steepest curvature. Even when the ridges are stretched in an oblique direction in the developing step to become linear, therefore, the apex 2e of each ridge remains to be elastically deformed and hence cannot be stretched into a fully linear form. When the wires 2b are stretched in the developing step, consequently, the tensile stress in this process is easily concentrated in both sides of the elastically deformed portion of the apex 2e which is bent.
In practice, the wires 2b are developed in the developing step not only by being obliquely stretched to become linear, also by being twisted at the ends in opposite directions as indicated by the arrows D and E in FIG. 45. As shown in FIG. 39(a) or FIGS. 47(a) and 47(c), in each of the nodes 2c, the sides in the width direction of the metal sheet 2 are vertically pressed in opposite directions by the valleys 1b of the upper and lower the disk cutters 1. Therefore, a level difference which approximately corresponds to the thickness of the sheet is formed between one side in the width direction and the other side, and also positions where the wires 2b are drawn out are different in level. As shown in FIG. 45, in a node 2c which is connected to one end of a certain wire 2b, one side in the width direction is higher in level, and the other side is lower. By contrast, in another node 2c which is connected to the other end of the same wire 2b, one side in the width direction is lower in level, and the other side is higher. When the metal sheet 2 is stretched in the width direction, therefore, the nodes 2c are stretched toward both the sides in the width direction by the wires 2b which are different in level, with the result that the nodes 2c, 2c which are shown in right upper, and left lower portions of FIG. 45 are twisted in the direction of the arrow F, and in contrast the nodes 2c, 2c which are shown in left upper, and right lower portions of FIG. 45 are twisted in the opposite direction or the direction of the arrow G. The wire 2b between the right upper and left upper nodes 2c, 2c is developed while the ends are twisted in opposite directions or the directions of the arrows D and E, respectively. As a result, each of the wires 2b is stretched while the ends are twisted in opposite directions, so that the torsion stress is easily concentrated in both sides of the elastically deformed portion of the apex 2e. 
In each of the wires 2b, consequently, the tensile stress and the torsion stress in the developing step are concentrated on both the sides of the elastically deformed portion of the apex 2e which remains to be bent, and a constricted part may be formed. Therefore, a grid which is produced by using a conventional rotary expander has a problem in that rupture often occurs in the portion. In the case where the metal sheet 2 is thick or has a thickness larger than 1.0 mm, or the case where the disk cutters 1 in which the ridges 1a largely protrude are used, particularly, rupture often occurs in the vicinity of the apex 2e of each wire 2b. When a battery is produced by using such a grid as a battery plate, local corrosion occurs in the rupture portion, or in the worst case a crack of corrosion occurs the wires 2b, thereby causing the life of the battery to be shortened. The invention has been conducted in order to cope with the above-discussed circumstances. It is an object of the invention to provide a grid for a battery plate in which an inclined face is formed on a peripheral side face of each ridge of a disk cutter, and wires are formed in a ridge-like shape in a state where the wires are pretwisted, thereby causing the wires to hardly rupture, and also a method of producing the grid.
Problem (4) to be Solved by the Invention
The shape of the disk cutter 1 and production steps in the production of a grid for a battery plate in which disk cutters for a rotary expander are used are shown in FIGS. 37 to 40. In a process of producing the grid for a battery plate, the slits 2a and the nodes 2c are formed in the metal sheet 2. As apparent from FIG. 46(a), the cutting is conducted while pressing each of the nodes 2c against a ridgeline 1k of the portion of the disk cutter 1 where the groove 1c of the peripheral side face of the valley 1b is formed. As shown in FIG. 46(b), therefore, stress is concentrated on the portion against which the ridgeline 1k is pressed, and rupture sometimes occurs in the node 2c. When such rupture once occurs, corrosion advances with starting from the rupture, and crack of corrosion finally occurs, thereby producing a problem in that the capacity of a lead storage battery is reduced or the life of the battery is shortened.
The invention has been conducted in order to cope with the above-discussed circumstances. It is an object of the invention to provide a method of producing a grid for a battery in which stress concentration is relaxed and rupture hardly occurs in the node 2c, and a battery using the grid for a battery.
Problem (5) to be Solved by the Invention
In the formation of the nodes 2c and the endmost nodes 2f of the metal sheet 2, as shown in FIGS. 47(a) and 47(c), the sides in the width direction are vertically pressed in opposite directions by the valleys 1b and 4b of the upper and lower disk cutters 1 and the endmost disk cutters 4 in which the grooves 1c are opposed to each other. Therefore, the sides in the width direction are vertically deformed with respect to each other by a large degree corresponding to the thickness of the metal sheet 2 or more, and the metal sheet 2 of the endmost nodes 2f is stretched to be thinned in accordance with the deformation. When the metal sheet 2 is stretched toward both the sides in the width direction, development is conducted while the wires 2b drawn out from the nodes 2c and the endmost nodes 2f which are thinned by the vertical deformation are laterally pulled to be obliquely bent. Therefore, stress is concentrated on the nodes 2c and the endmost nodes 2f, and the possibilities that rupture occurs during a production process, and that, after a battery is produced by using such a grid for a battery, a crack of corrosion is caused between the nodes and the wires 2b by corrosion or heat are increased. When a crack of corrosion of the wires 2b occurs in one of the endmost nodes 2f connected to the frame portions 2g of the metal sheet 2 where a lug of the grid is formed for current collection from the battery plate, the plate portion that is on the other side in the width direction is connected to the lug through a detour. As a result, the current hardly flows, so that disadvantages such as that the active material in the portion is not effectively used, and that a large current flows through the detour to generate heat are largely increased. When a crack of corrosion occurs in any one of the nodes 2c other than the endmost nodes 2f, similarly, a current hardly flows from the plate portion that is on the other side in the width direction with respect to the node 2c. However, influence due to the above is more extremely reduced as the node 2c is more separated from the frame portions 2g where a lug is formed.